Radio direction finding system



` April 1.3, 1937. H. M.' DoweiETT ET AL 076710 RADIO DIRECTION FINDINGSYSTEM Original Filed May 18, 1933 ATTORNEY `55`aerial or, where aBellini Patented Apr. 13, 1937 ATE.

oFFlca RADIO DIRECTION FINDING SYSTEM Harry Melville Dowsett,

and Roland John Kemp;

Winchmore Hill, London, Chelmsford, England,

assignors to Radio Corporation of America, a corporation of DelawareApplication May 1s, Renewed June 14, 1 25, 1932.

'7 Claims.

This invention relates to radio direction .iinding systems and has forits object to provide an improved receiver arrangement wherein thedirection of a radio beacon or other transmitting station is indicatedby the clear reception of a television picture.

A further object of the invention is-to provide an improved systemwherein the level of the synchronized impulses provided at the receiverfor synchronizing the receiving television scanning apparatus with thetransmitting television scanning apparatus shall be received at asubstantially constant level.

, Arrangements wherein television transmission i and'reception areemployed for direction finding purposes are described in thespecifications accompanying co-pending application Serial No.672,552,'filed May 24, 19331 It is very desirable for practical reasonsthat when a receiving station equipped with.A television apparatus andemployed for bearing finding and directional purposes has its receivingaerial system correctly oriented to obtain a bearing on a particularbeacon or transmitter, the received television picture obtained fromthat beacon or transmitter should appear` clearly and the principalobject of the presentjnvention is to provide an improved receiverarrangement whereby this is achieved, the received picture being onlyreceived soclearly when the aerial system is correctly oriented orapproximately correctly oriented and the character of the said receivedpicture clearly visibly different for other orientations of thereceiving directional aerialsystem.

According to this invention a receiving television station for use forbearing finding and similar purposes comprises a frame or equivalentdirectional receiving system, an open aerial or equivalent substantiallynon-directional receiving 40 system, a television scanning and picturesynthesizing system, means for building up by means of said scanningandpicture synthesizing system a picture derived from signals receiveduponv the substantially non-directional aerial system, and

means for superimposing upon said signals, signals of reverse phasederived from the directional aerial system.v`

The directional aerial system may take any convenient form: for example,it may be constituted i by a rotatableframe aerial or by a Bellini-TosiaerialsystemY in co-operationwith a radiogoniometer and similarlyV thesubstantially non-directional aerial systemlmay take diierent forms, forexample, it may be constitutedsimply by an open -Tosi directional system1933, Serial No. 671,646. 935. In Great Britain May (Cl. Z50-11) isemployed, the vertical effect of said system may be utilized in mannerknown, per se, for non-directional reception.

The phase reversal of the signals from the directional system withrespect to those from the non-directional system may be obtained in anyconvenient way, for example, a low frequency arnplirler following thedetector energized from the directional system may contain one more orone l less stage oi magnification than the corresponding low frequencyamplier following the detector energized from the non-directional aerialsystem or, again, the type of detection employed for the signalsreceived from the directional system may be different from that employedfor the signals from the non-directional system, leak grid detectionbeing employed for one set of signals and anode bend detection forrtheother.

It will be seen that with arrangements in ac-, cordance with the presentinvention the signals" received by the directional system will besubstantially non-existent when that system is correctly oriented to thedirection of the station being received, and in carrying out the presentinvention` the arrangement is preferably made such thatt Awithin apredetermined number of degrees of the correct bearing direction, e.,g.within 10 degrees of that direction, thestrength of signals receivedfrom the directional aerial system is approxi-V l lmately the same asthat from the'non-direc-A tional system. Thus, since the effect of thesu- ,perimposition in the picture synthesizing apparatus of the signalsreceived from the directional system upon those received from thenon-direck tional system is is, as it were, a negative of the picturefrom said non-directional system, it will be apparent that within thepredetermined limit of 10 degrees or thereabouts there will be a sharpcontrast in the total received picture as between the combined positiveand negative pictures obtained when the signals from both `aerialsystems are about the same strength and the clear positive picureobained at the correct bearing position when the signals from thedirectional system are'substan-'U tially non-existent. Y

The invention is illustrated in the accompanying diagrammatic drawingwhich shows a rreceiving station in accordance therewith.

Referring to the drawing a tuned rotating frame aerial A tuned by acondenser as shown is employed as the directional system and the signalsobtained therefrom are applied, after r amplification at the carrierfrequency by means of a Valve V1, between the grid and cathode of a Y tosuperimpose a picture whigh..H

lamp GL breaks down nizing pulses, which are of an amplitudesubstanthermionic valve Va to which the requisite potentials are appliedto cause said valve to operate as an anode bend detector. This detectorvalve is resistance capacity coupled to a triode V3 in cascade therewithand acts as a common amplier both`- for `the directionally receivedsignals and thenon-directionally received signals. The non-directionallyreceived signals are picked up upon a vertical aerial B which is tunedin the usual Way by a condenser as shown,- the signals from this aerialbeing applied, after amplification at the carrier frequency, if desired,between the grid and cathode of a triode Vi in whoseA grid lead isinserted the usual grid condenser GC and grid leak GL so as to causesaid triode to operate as a leaky grid detectormThis detectorisresistance-capacity coupledt'o a further ltriode V5 whose output isresistance-capacity coupled to the aforementioned common triode amplierV3. The output from the common amplier is further amplified, if desired,e. g., by valves Ve, V7 and applied to a4 neon lamp NL 0r equivalentpicture building device incorporatedin the television picturesynthesizing apparatus. 'I'he output from the detector Vi energized fromthe open aerial system B is also applied to a vfurther amplifiercontaining any predetermined number of stages, this amplifier beingadapted toselect and amplify the synchronizing signals for thetelevision transmission and to apply these amplified synchronous signalsto control the electric motor or like device, not shown, drivingand/ orsynchronizing ythe television scanning apparatus. In the figure thisfurther ampliiier consists of two valve stages Vs, V9 coupled togetherin cascade. vThe valve V8 has in, its plate circuit a neon lamp orotherglow kdischarge lamp 'GL' and the ignition voltage of this lampissuch and the remaining constantsof the circuit are such that the saidonly when the synchrotially greater than rthe peak amplitude of thepicture signals, appear in the anode circuit of the valve Vs. Thus thevalve V9 is energized by synchronizing pulses onlyvand the output fromthis valve is employed. for energizing the synchronizing winding, notshown, of the motor driving the television scanning apparatus, notshown. It will be seenthat with the above described arrangement when thesignals from the aerials A` Vandrlare equal or nearly equal, the resultof their mixture in ranti-phase at the grid of the Valve V3 will besuchas nearly to eliminate any image, e., there will not be a clearpicturebuilt up by the lamp NL. When, however, the frame aerial at A isrturnedin such a direction that the signalsv picked up thereby approximate tozero, a clear positive picture will be built up vby the lamp NLvand theexistence of this clear positive picture will indicate that the frameaerial has been turned in the direction of the station being received.r01 course, the rotatable frame aerial may be replaced by mutuallyperpendicular xed frames associated with a radiogoniometer. A receivingstation in accordance withy the present invention may be employed toreceive signals from transmitting stations as described in thespecication of cti-pending application Serial No. 672,5 52 abovereferred to for example, the transmitt'er may be Such that the majorlintelligence comprising an image of a moving scale station,identification letters, and synchronizing impulses are transmitted byan'` o'nini-directional aerial 5 and a I'ninimunfi` indicating signal,such as a vertical bar appearing across the picture, is transmitted by arevolving frame.

Where a receiver in accordance with the present invention is utilized inconjunction with a transmitter as just described the minimum indicatingsignal, thevertical bar, will appear clearly onlyvwhren the receivingframe is correctly oriented towards the transmitting station.

i Having thus described our invention and the operation thereof, what weclaim is:

1. A receiving television station for use for bearing finding andsimilar purposes comprising, a frame or equivalent directional receivingsystem, an open aerial or equivalent substantially non-directionalreceiving system, a television scanning and picture synthesizing system,circuits connecting the receiving systems and the television andsynthesizing system, means for building up by means of said scanning andpicture synthesizing system a picture derived from signals received uponV,the substantially nondirectional aerial system, and means forAsuperirnposing upon said signals, signals of reverse phase derived fromthe directional aerialgsy'stem.

2. A receiving station as claimed in claim 1 comprising in addition adetector connected with the directional system and a. low frequencyampliiier following the detector ,energized from the directionazl systemfor producing the phase reversal.

3.v Aj receiving., station as claimed in claim 1 comprising in additionmeans for obtaining the required phase reversal comprising `diiierenttypes of Idetection means for detecting the signals received yfrom thedirectional system and from the non-directionalsystem respectively. i

v4. A receivifg station as claimed in claim 1 comprising in additionmeans for independently and separately detecting the signals receivedupon the` non-directional aerial system and upon the directional aerialVsystem means for combining the outputs from the two detectors, inAantiphase relation, and a common amplier for amplifying the combinedsignals for controlling the picture reproducing device of the televisionreceiver. i

5. A station f or receiving wave energy on which synchronized impulseshave been impressedin addition tc the television signals comprising adirectional aerial, a vertical aerial, a television scanning and picturesynthesizing system, signal relaying circuits connecting lthe aerialsystems to the ,television and synthesizing system, driving means forsaid television scanning and picture synthesizing system, means forbuilding up by means of said scanning and picture synthesizing systernapicture derived from the relay connected with the vertical aerial, meansfor superimposing upon said signals, signals of reverse phase derivedfrom the relay circuit connected with the directicnal aerial, meansconnected with the relay connectedto the vertical aerial for separatingthe synchronizing impulses from the signals picked up by the verticalaerial, and means for utilizing said impulses for synchronizing thedriving means for thereceiving television scanning system..

6. The method of receiving the wave energy of asingle carrier frequencyon which synchronizing impulses and electro-optical representations areimpressed by modulation which includes the steps of setting uposcillatory energy characteristic of the electro-optically modulatedcarrier wave energy and of the direction of propagation of said waveenergy, setting up oscillatory energy characteristic of the carrier waveenergy modulated by synchronizing impulses and non-characteristic of thedirection of propagation of said wave energy, and combining saidenergies to produce Visual representations characteristic of thedirection of propagation of said energy, and controlling said combiningin accordance with the impulses in said oscillations non-characteristicof the direction of propagation of said Wave.

7. A receiving television station for use for bearing finding andsimilar purposes comprising a frame aerial or equivalent directionalreceiv- 10 ing system, an open aerial or equivalent substan-

